Design and Analysis of Pulse Tube Refrigerator

Abstract

After decades of rapid development, the absence of moving parts in the cold head, low vibration, long lifetime and high reliability, pulse tube refrigerators are the most promising cryo-coolers. Because of these momentous advantages, they are widely used in Superconducting Quantum Interference Devices (SQUIDs), cooling of infrared sensors, low noise electronic amplifiers, missiles and military helicopters, superconducting magnets, liquefaction of gases, gamma ray spectrometers, liquefaction of gases, X-ray devices and high temperature superconductors etc. It has also got wide applications in preservation of live biological materials as well as in scientific equipment. It is essential to accurate modelling of the pulse tube cryocooler and predicts its performance, thereby arrive at optimum design. At the current stage of worldwide research, such accurate models are not readily available in open literature. Further, the complexity of the periodic flow in the PTR makes analysis difficult. Although different models are available to simulate pulse tube cryocoolers, the models have its limitations and also range of applicability. In order to accurately predict and improve the performance of the PTR system a reasonably thorough understanding of the thermos fluid- process in the system is required. One way to understand the processes is by numerically solving the continuum governing equations based on fundamental principles, without making arbitrary simplified assumptions. The recent availability of powerful computational fluid dynamics (CFD) software that is capable of rigorously modelling of transient and multidimensional flow and heat transfer process in complexgeometries provides a good opportunity for analysis of PTRs. Performance evaluation and parametric studies of an Inertance tube pulse tube refrigerator (ITPTR) and an orifice pulse tube refrigerator (OPTR) are carried out. The integrated model consists of individual models of the components, namely, the compressor, after cooler, regenerator, cold heat exchanger, pulse tube, warm heat exchanger, inertance tube or orifice, and the reservoir. In the first part of the study, the commercial CFD package, FLUENT is used for investigating the transport phenomenon inside the ITPTR. The local thermal equilibrium and thermal non-equilibrium of the gas and the matrix is taken into account for the modelling of porous zones and the results are compared. The focus of the second part of the study is to establish the most important geometrical dimension and operating parameters that contribute to the performance of ITPTR and OPTR. The numerical investigation procedure for these investigations is conducted according to the Response surface methodology (RSM) and the results are statistically evaluated using analysis of variance method. Finally a multi-objective evolutionary algorithm is used to optimize the parameters and for an optimized case the phasor diagram is discussed.